Buffer gas cooled ice chemistry. I. Buffer gas cell and mm-wave spectrometer

Radhakrishnan, Soumya; Hager, Travis; Kanaherarachchi, Anudha; Williams, Christopher; Hall, Gregory E.; Broderick, Bernadette M.

doi:10.1063/5.0111792

Cited by 3 publications

(6 citation statements)

References 29 publications

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“…Following ∼9 collisions with cold Ne atoms in the BGC, the desorbed species are cooled and detected with broadband millimeter-wave radiation . A schematic of the 60–90 GHz spectrometer is given in Figure , and a detailed description of the CPICE data acquisition system is provided in ref . The fast on-board averaging at 10 GS/s in CPICE lends itself well to TPD measurements given that a finite number of molecules are present within the ice sample in each experiment and desorb within a narrow temperature window.…”

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confidence: 99%

“…In addition to condensed-phase studies, CPICE is also equipped to probe gas-phase molecules which are initially at room temperature and directly injected into the BGC . This permits a comparison of the gas-phase abundances observed with those measured following sublimation off an ice surface.…”

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confidence: 99%

“…In addition to condensed-phase studies, CPICE is also equipped to probe gas-phase molecules which are initially at room temperature and directly injected into the BGC. 37 This permits a comparison of the gas-phase abundances observed with those measured following sublimation off an ice surface. Current astrochemical models, which are central to our understanding of the chemistry of icy grains, rely heavily on gas-phase information given the lack of experimental data available in the condensed phase.…”

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Conformer-Specific Desorption in Propanol Ices Probed by Chirped-Pulse Millimeter-Wave Rotational Spectroscopy

Borengasser,

Hager,

Kanaherarachchi

et al. 2023

J. Phys. Chem. Lett.

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We present a new technique for the detection of molecules desorbed from an ice surface using broad-band millimeter-wave rotational spectroscopy. The approach permits interrogation of molecules that have undergone the slow warmup process of temperature-programmed desorption (TPD), analogous to the warmup phase of icy grains in the interstellar medium as they approach the central protostar. The detection is conformer-and isomer-specific and quantitative, as afforded by chirped-pulse rotational spectroscopy. To achieve this, we combine ice TPD with buffer gas cooling, followed by detection in the millimeter-wave regime. In this report we examine the TPD profiles of n-and i-propanol, the former of which may be in five different conformational isomeric forms, and which display distinct desorption profiles. The limited conformational isomerization and temperature-dependent relative yields of n-propanol conformers observed show that the desorption is highly conformer-specific.

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Conformer-Specific Desorption in Propanol Ices Probed by Chirped-Pulse Millimeter-Wave Rotational Spectroscopy

Borengasser,

Hager,

Kanaherarachchi

et al. 2023

J. Phys. Chem. Lett.

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“…37 In previous work, we showed the successful application of this technique for the gas-phase injection of n-PrCN, where we examined anti-n-PrCN and gauche-n-PrCN to determine the rotational temperature of molecules within a 25 K cell. 38 In our most recent work with normal-and iso-propanol (PrOH), we applied CPICE to study molecules desorbing from an ice surface over the course of temperature-programmed desorption (TPD). 36 This previous work revealed surprising conformer-specific desorption profiles and quantified the relative abundances of conformers and isomers following both room-temperature gas-phase injection and separately following TPD of PrOH ices generated at 4 K. The results showed that the relative conformer yield varied dramatically during desorption, likely reflecting the composition of the ice itself.…”

Section: ■ Introductionmentioning

confidence: 99%

“…While cold, these molecules are subjected to broadband excitation pulses resulting in the detection of highly resolved molecular signals via rotational transitions immediately following desorption . In previous work, we showed the successful application of this technique for the gas-phase injection of n -PrCN, where we examined anti-n -PrCN and gauche - n -PrCN to determine the rotational temperature of molecules within a 25 K cell . In our most recent work with normal - and iso -propanol (PrOH), we applied CPICE to study molecules desorbing from an ice surface over the course of temperature-programmed desorption (TPD) .…”

Section: Introductionmentioning

confidence: 99%

Conformer Distributions of n-Propyl Cyanide in the Gas Phase and Following Ice Sublimation Measured by Broadband Rotational Spectroscopy

Kanaherarachchi,

Hager,

Borengasser

et al. 2024

ACS Earth Space Chem.

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The conformer distribution of normal-propyl cyanide is investigated using broadband chirped pulse rotational spectroscopy in the millimeter-wave regime coupled with buffer gas cooling. Here we explore the relative abundances of the anti and gauche conformers following room-temperature gas-phase injection into a 25 K buffer gas cell and compare to that which is observed following temperatureprogrammed desorption from an ice surface, similar to the slow warm-up experienced by ice grains as they approach warmer regions within the interstellar medium. The conformer distributions observed in the gas phase from roomtemperature injection are then used to determine their relative energies, an important parameter needed to interpret the isomer and conformer abundances derived from astronomical observations. We find the gauche conformer to be the most stable species by ∼97 ± 21 cm −1 . We further examine the relative conformer abundances following ice desorption, which are distinct from those following the gas-phase introduction. The ratios measured off the ice correspond to a conformer temperature of ∼56 K, which is much lower than their sublimation temperature of 170 K.

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Low temperature reaction kinetics inside an extended Laval nozzle: REMPI characterization and detection by broadband rotational spectroscopy

Thawoos,

Suas-David,

Gurusinghe

et al. 2023

The Journal of Chemical Physics

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Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF (“Chirped-Pulse/Uniform flow”). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20 K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20 K of 6.66 ± 0.47 × 10−11 cm3 molec−1 s−1.

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Buffer gas cooled ice chemistry. I. Buffer gas cell and mm-wave spectrometer

Cited by 3 publications

References 29 publications

Conformer-Specific Desorption in Propanol Ices Probed by Chirped-Pulse Millimeter-Wave Rotational Spectroscopy

Conformer-Specific Desorption in Propanol Ices Probed by Chirped-Pulse Millimeter-Wave Rotational Spectroscopy

Conformer Distributions of n-Propyl Cyanide in the Gas Phase and Following Ice Sublimation Measured by Broadband Rotational Spectroscopy

Low temperature reaction kinetics inside an extended Laval nozzle: REMPI characterization and detection by broadband rotational spectroscopy

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